3-Bacterial Metabolism and Genetics Flashcards
What are obligate anaerobes?
Oxygen (O2 gas), although essential for the human host, is actually a poison for many bacteria. Some organisms, such as Clostridium perfringens, which causes gas gangrene, cannot grow in the presence of oxygen. Such bacteria are referred to as obligate anaerobes.
What are obligate aerobes?
Other organisms, such as Mycobacterium tuberculosis, which cause tuberculosis, require the presence of molecular oxygen for growth and are therefore referred to as obligate aerobes.
What are faculative anaerobes?
Most bacteria, however, grow in either the presence or the absence of oxygen. These bacteria are referred to as facultative anaerobes.
What occurs during the lag phase of bacterial growth?
lag phase: initial part of the curve, there is no increase in cell number (horizontal graph line)
small increase in curve between phases
What occurs during the exponential phase of bacterial growth?
exponential phase: next part where the cell number increases in an exponential fashion (however, slope of graph is linear) as time increases. The bacteria will grow and divide with a doubling time characteristic of the strain determined by the conditions. The number of bacteria will increase to 2 to the nth power, in which n is the number of generations or doublings
small decrease in slope between phases
What occurs during the stationary phase of bacterial growth?
stationary phase: next part of curve where there is no increase in cell number with respect to time (horizontal graph line) because it runs out of metabolites, or a toxic substance builds up in the medium
small gap between phases where graph descends linearly
What occurs during the decline phase of bacterial growth?
decline: last part of graph where cell growth declines exponentially (linear graph line) with respect to time.
What is an operon?
An operon is a functioning unit of key nucleotide sequences including an operator, a common promoter, and one or more structural genes, which are controlled as a unit to produce messenger RNA (mRNA), in the process of protein transcription. Operons are groups of one or more structural genes expressed from a particular promoter and ending at a transcriptional terminator. Thus all the genes coding for the enzymes of a particular pathway can be coordinately regulated.. The organization of the genes of a biochemical pathway into an operon, with appropriate genetic control mechanisms, allows coordinated production of the necessary enzymes in response to a nutritional stimulus.
What are plasmids?
Plasmids carry genetic information, which may not be essential but can provide a selective advantage to the bacteria. For example, plasmids may confer high levels of antibiotic resistance, encoding the production of bacteriocins, toxins, virulence determinants, and other genes that may provide the bacteria with a unique growth advantage over other microbes or within the host. The number of copies of plasmid produced by a cell is determined by the particular plasmid. The copy number is the ratio of copies of the plasmid to the number of copies of the chromosome. This may be as few as one in the case of large plasmids or as many as 50 in smaller plasmids.
What are cistrons?
Genes are sequences of nucleotides that have a biologic function; examples are protein-structural genes (cistrons, which are coding genes), ribosomal ribonucleic acid (RNA) genes, and recognition and binding sites for other molecules (promoters and operators).
What does “polycistronic” mean?
Operons with many structural genes are polycistronic. Example E. coli lac operon which includes all the genes necessary for lactose metabolism as well as the control mechanisms for turning off or turning on these genes when needed
What is an episome?
An episome is a plasmid that can be integrated into the host chromosome. In this situation, it can stay intact for a long time, be either diluted out or be duplicated with every cell division of the host, and become a basic part of its genetic makeup. The term is no longer commonly used for plasmids, since it is now clear that a region of homology with the chromosome such as a transposon will make a plasmid into an episome. In mammalian systems, the term episome refers to a circular DNA (such as a viral genome) that is maintained by noncovalent tethering to the host cell chromosome
What is the Ori C?
Replication of bacterial DNA is initiated at specific sequence in a chromosome called Ori C
What is a pathogencity island?
Some pathogenic bacteria use a transposon-like mechanism to coordinate the expression of a system of virulence factors. The genes for the activity may be grouped together in a pathogenicity or virulence island, which is surrounded by transposon-like mobile elements, allowing them to move within the chromosome and to other bacteria. The entire genetic unit can be triggered by an environmental stimulus (e.g., pH, heat, contact with the host cell surface) as a way to coordinate the expression of a complex process. For example, the SPI-1 island of Salmonella encodes 25 genes that allow the bacteria to enter nonphagocytic cells
What is transformation?
Transformation is the process by which bacteria take up fragments of naked DNA and incorporate them into their genomes.
